1. Field of the Invention
The present invention relates to a lens barrel of an imaging apparatus, and in particular, relates to a drive mechanism for moving (driving) a lens group that constitutes a photographing optical system in an optical axis direction thereof.
2. Description of the Related Art
In a lens barrel provided with at least one lens group, of a photographing optical system, which is moved in an optical axis direction thereof to carry out a zooming operation and/or a focusing operation, there have been numerous countermeasures taken in order to prevent damage and/or breakage of the lens group and the drive mechanism therefor even in the case where a mechanical or control error of some kind occurs during the driving (moving) of the lens group.
One known example of such a countermeasure, in a lens barrel provided with a first drive system which controls the position of a lens support frame via a cam mechanism, provided with a cam ring which is rotatably driven by a motor, and a second drive system which controls the position of another lens support frame by a feed screw and a nut which are rotatably driven via another motor, is an arrangement which prevents overloading caused by interference between the lens groups (and/or the lens support frames thereof) that are driven by the first and second drive systems.
The first drive system is often used for driving (moving) a lens group to carry out a zooming operation in a zoom lens system barrel provided with a cam follower on a lens support frame (or a member that supports a lens support frame) which is engaged with a cam groove (including a lead groove, etc., in addition to a curved-profile cam groove) formed in a peripheral surface of the cam ring, and the lens support frame is moved (advanced and retracted) in the optical axis direction in accordance with the contours of the cam groove upon rotatably driving the cam ring.
The second drive system is often used for driving (moving) a focusing lens group and includes a feed screw which is formed on a rotational axis of a motor and extends in the optical axis direction, and the lens support frame (of the focusing lens group) which is movably guided in the optical axis direction is biased to be brought into contact with a nut that is screw-engaged with the feed screw. By forwardly/rearwardly moving the nut along the thread of the feed screw, the nut presses and moves the lens support frame in a direction against the biasing force, and the lens support frame follows the nut by the biasing force in the other direction.
If countermeasures are taken so that the operational (movement) range of the lens group of the first drive system and the operational (movement) range of the lens group of the second drive system do not mutually overlap each other, the lens groups (and the lens support frames thereof) that are respectively driven by the first and second drive systems do not mutually interfere with each other even if an unexpected out-of-control movement, etc., of the nut occurs in the second drive system. However, in such an arrangement, a problem exists with the size (the length in the optical axis direction in particular) of the lens barrel increasing in order to obtain a large amount of movement space for each lens group; hence, such arrangement is especially unsuitable for a lens barrel which retracts (shortens its length) in order to be accommodated in a camera body when in a fully-retracted state. Furthermore, there are many instances where, from the viewpoint of optical design, the lens group movement ranges of the first and second drive systems cannot be completely excluded from each other (i.e., cannot be made different so as not to overlap each other) with respect to the optical axis direction.
Accordingly, in a lens barrel in which the movement ranges of the lens groups partially overlap each other between the first and second drive systems, the lens barrel was configured while paying attention to the fact that in the second drive system the movement of the lens support frame is not mechanically restricted in a direction away from the nut (a direction against the biasing force), so that the lens support frame can escape in a direction away from the nut in the case where an operational malfunction, etc., occurs. In other words, the lens support frame (designated as a first lens support frame) that is driven (moved) by the first drive system is provided at a position on the biasing-direction side of the lens support frame (designated as a second lens support frame) that is driven (moved) by the second drive system, in the case where the first and second lens support frames come on contact with each other, the second lens support frame is pushed by the first lens support frame in a direction against the biasing force. Since the movement of the second lens support frame in this direction (against the biasing force) is not restricted by the nut, an excessive load can be avoided from being exerted on the first drive system and the second drive system. Specifically, an arrangement is known in the art in which the second lens support frame is provided at the rearmost position (closest to the image side) in the optical axis direction and is biased forwardly (toward the object side) in the optical axis direction so that the second lens support frame is brought into contact with the nut, and the first lens support frame is provided in front (on the object side) of the second lens support frame. In this arrangement, during a lens barrel accommodation operation (lens barrel retracting operation), in the case where the second lens support frame does not correctly move rearwardly in the optical axis direction via the nut when it should, the first lens support frame, which is carrying out a lens barrel accommodation operation while rearwardly moving in the optical axis direction, pushes the second lens support frame so that the first and second lens support frames both move rearwardly in the optical axis direction. Furthermore, in the case where the second lens support frame moves forwardly in an out-of-control manner in the optical axis direction so that the nut exceeds the restricted movement amount thereof, the movement of the second lens support frame is restricted by the second lens support frame coming into contact with the first lens support frame, so that only the nut is allowed to move forward thereafter without inflicting excessive load on the first and second lens support frames.
Examples of the related art are disclosed in Japanese Unexamined Patent Publication Nos. 2007-248642 and 2010-191442.
In the above-described arrangement in which the first lens support frame that is driven by the cam mechanism is provided at a position on the biasing-direction side of the second lens support frame that is driven by the feed screw and the nut (so that the lens support frame and the nut move away from each other in the optical axis direction in the case where an operational malfunction, etc., occurs), such an arrangement is effective in the case where no other interfering member exists on the reverse side of the position on the biasing-direction side of the second lens support frame. However, there is a demand to achieve a higher zoom ratio and an improved optical quality of the zoom lens system without having such restrictions, in which it is desired for the first lens support frame that is driven by the cam mechanism to also be provided on the reverse side, with respective to the biasing-direction side, of the second lens support frame that is driven by the feed screw and the nut.